Add gh release workflow

.github/workflows/release.yml

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+name: Release
+on:
+  push:
+    branches:
+      - main
+      - "v[0-9]+.[0-9]+"
+    tags:
+      - "v*"
+
+env:
+  RUST_VERSION: 1.86
+
+jobs:
+  crates:
+    name: Publish to crates.io
+    runs-on: ubuntu-latest
+    if: |
+      startsWith(github.ref, 'refs/tags/v') &&
+      github.repository_owner == 'fermyon'
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install Rust toolchain
+        shell: bash
+        run: |
+          rustup toolchain install ${{ env.RUST_VERSION }}
+          rustup default ${{ env.RUST_VERSION }}
+
+      - name: Publish wasi-hyperium to crates.io
+        working-directory: ./
+        run: |
+          cargo publish --token ${{ secrets.CARGO_REGISTRY_TOKEN }}

RELEASE.md

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+# Cutting a new release of wasi-hyperium
+
+To cut a new release, you will need to do the following:
+
+1. Confirm that [CI is green](https://github.com/fermyon/wasi-hyperium/actions) for the commit selected to be tagged and released.
+
+2. Change the workspace version number in [Cargo.toml](./Cargo.toml).
+
+3. Create a pull request with these changes and merge once approved.
+
+4. Checkout the commit with the version bump from above.
+
+5. Create and push a new tag with a `v` and then the version number.
+
+    As an example, via the `git` CLI:
+
+    ```
+    # Create a GPG-signed and annotated tag
+    git tag -s -m "wasi-hyperium v0.3.0" v0.3.0
+
+    # Push the tag to the remote corresponding to fermyon/wasi-hyperium (here 'origin')
+    git push origin v3.1.0
+    ```
+
+6. Pushing the tag upstream will trigger the [release action](https://github.com/fermyon/wasi-hyperium/actions/workflows/release.yml) which publishes the crates in this workspace to `crates.io`.